In the material which follows, the time points "intake open" and "intake close" will be used and relate to the particular crankshaft angle differences referred to top dead center of a piston at the beginning of an intake stroke or to bottom dead center at the end of an intake stroke. The statement that a time point such as "inlet open" is constant means that for all cylinders, the crankshaft angle difference mentioned above is the same.
A method of controlling a four-stroke spark-ignition engine without a throttle flap is disclosed in the article by J. H. Tuttle entitled "Controlling Engine Load by Means of Early Intake Valve Closing", SAE-Paper 820408 (1982), pages 1 to 15. In order to obtain different intake volumes notwithstanding the absence of the throttle flap, the time points "inlet close" were varied for each constant time point "inlet open".